3-D volume imaging has proved to be a valuable diagnostic tool that offers significant advantages over earlier 2-D radiographic imaging techniques for evaluating the condition of internal structures and organs. 3-D imaging of a patient or other subject has been made possible by a number of advancements, including the development of high-speed imaging detectors, such as digital radiography (DR) detectors that enable multiple images to be taken in rapid succession.
Cone beam computed tomography (CBCT) or cone beam CT technology offers considerable promise as one type of diagnostic tool for providing 3-D volume images. Cone beam CT systems capture volumetric data sets by using a high frame-rate digital radiography (DR) detector and an x-ray source, typically affixed to a gantry that rotates about the object to be imaged, directing, from various points along its orbit around the subject, a divergent cone beam of x-rays toward the subject. The CBCT system captures projections throughout the rotation such as, for example, one 2-D projection image at every degree of rotation. The projections are then reconstructed into a 3D volume image using various techniques. Among well known methods for reconstructing the 3-D volume image from the 2-D image data are filtered back-projection approaches.
Although 3-D images of diagnostic quality can be generated using CBCT systems and technology, a number of technical challenges remain. The Applicants have recognized that one difficulty with obtaining suitable 3D volume images relates to patient pose. Inappropriate patient pose can cause various problems, for example:
(i) Inadvertent truncation of the anatomy. If the toes of a foot, for example, lie outside of the volume of interest (VOI), noticeable truncation artifacts can be induced and may significantly degrade the image quality and the Hounsfield Unit (HU) accuracy of the resulting images.
(ii) Poor alignment. If the body part being imaged is not well aligned with the reconstruction volume, the sagittal/coronal views that result can be tilted. This problem can make it difficult for the practitioner to analyze the images.
(iii) Inappropriate pose of the patient. When measuring three-dimensional morphological characteristics of the anatomy, the patient pose may not match a reference pose or standard pose that provides suitable information on the patient condition. If this is the case, the quantitative results (e.g., distance/angle between two bones) may not be readily comparable to established, reference values that facilitate proper assessment. Under some conditions with inappropriate positioning, patients might even need to undergo a repeated X-ray exam, causing additional X-ray dose to the patient.
Thus, it can be appreciated that methods to facilitate visualization of patient anatomy in standard poses can be of value for assisting practitioner assessment of patient condition and can help to reduce ambiguity in diagnosis.